Luteal phase defect is when there is inadequate secretion or action of the hormone progesterone during the menstrual cycle. This results in a lag of more than two days in the development of the endometrium (the lining of the uterus, where an egg implants).

The concept of luteal phase defect is controversial, and its role in infertility is uncertain. It may affect about 3 to 4% of infertile women, and up to 5% in women with a history of recurrent, spontaneous abortions. However, luteal phase defect can be found in up to 30% of isolated cycles of normal women.

Risks factors include:

• A history of unexplained infertility
• A history of recurrent spontaneous abortions

Traditionally, a biopsy of the endometrium is the standard for diagnosing luteal phase defect. However, measuring the progesterone level in blood serum is often used as a means of diagnosis instead of endometrial biopsy due to the pain, difficulties of precise menstrual cycle dating, and expense associated with endometrial biopsy.

A blood serum progesterone level of lower than 10ng/mL one week prior to the start of menstruation or 7 days after the LH (luteinizing hormone) surge is generally accepted as a diagnosis of luteal phase defect.

Progesterone injections or gel (Crinone) are often used when luteal phase defect is suspected.

If there is evidence that low FSH (follicle stimulating hormone) is present with luteal phase defects, clomiphene citrate may also be used.

Using progesterone therapy, success rates of approximately 50% have been reported, but good controlled clinical studies are lacking. The risk of using clomiphene citrate is its uncertain effectiveness and a 5% chance of multiple births (mostly twins).